The present invention relates generally to the separation of zinc from zinc ore and, more particularly, to the flotation of zinc minerals from non-sulfide zinc ores using an ester of a mercaptocarboxylic acid as a collector.
Zinc is naturally found in association with lead in mixed lead-zinc ores which may or may not be sulphidic. Non-sulfide zinc ores include hemimorphite (basic zinc silicate) and smithsonite (zinc carbonate); hydrozincite (basic zinc carbonate); loseyite (basic zinc silicate) and willemite (zinc silicate). Various procedures have been employed to separate the zinc from the ore, flotation being one of the most commonly used. See, for example, U.S. Pat. Nos. 4,118,312 and 4,139,455 which issued to G. Barbery et al. on Oct. 3, 1978 and to R. M. Griffith et al. on Feb. 13, 1979, respectively. In such flotation procedures, the ore is first ground to a size sufficient to liberate the zinc mineral which is then introduced with a collector into a buoyant, air-bubble containing medium. Bubbles are produced in a flotation machine by mechanical agitation or by the direct introduction of air under pressure. The collector serves to enable the minerals to cling to the air bubbles.
Flotation has been successfully used commercially to separate zinc from mixed sulfide zinc ores; one such process being described, for example, in U.S. Pat. No. 3,235,077 which issued to P. E. McGarry et al. on Feb. 15, 1966.
The separation of zinc from non-sulfide zinc ores by flotation has proven somewhat less commercially practical. One such attempt is described in U.S. Pat. No. 2,482,859 which issued to W. J. McKenna et al. on Sept. 27, 1949 where a soluble compound of an aliphatic amine was used as a collector. The use of primary alkyl amines as collectors are taught in French Pat. Nos. 1,001,166; 1,011,183; 1,036,092 and provisional French Pat. No. 634,508. Other approaches include the use of amyl xanthate as a collector.
A particular problem presented in floating non-sulfide zinc ores is the presence of a slime which must be removed prior to or at an early stage of the processing. These slimes are very fine particulate matter, often silicates. The desliming operation may be accomplished mechanically such as, for example, by the use of a hydrocyclone. The disadvantage of any desliming operation is that it adds an additional step which is not only costly but, invariably may result in the loss of up to 40% of the zinc in the discarded slimes.
The use of flotation techniques for non-sulfide zinc ores requires the addition of a substantial amount of soluble sulfide. See, for example, McKenna U.S. Pat. No. 2,482,859, which employs between 6 and 12 pounds of sodium sulfide per ton of ore.
It has been found that by subjecting the ground ore to a selective flocculation step prior to flotation and utilizing an ester of a mercaptocarboxylic acid as a collector during flotation, concentration of the zinc may be accomplished without need for a separate desliming step and also require substantially smaller amounts of soluble sulfide than heretofore required, i.e. less than about two pounds per ton of ore. Since the loss of zinc in desliming is eliminated, zinc recovery is substantially improved.
Against the foregoing background, it is a primary objective of the present invention to provide a method for recovering zinc from non-sulfide zinc ores.
It is a further objective of the present invention to provide such a flotation method for non-sulfide zinc ores in which a desliming operation is not required.
It is another objective of the present invention to provide such a flotation method for non-sulfide zinc ores wherein a selective flocculation step is employed prior to flotation.
It is still another objective of the present invention to provide such a flotation method for non-sulfide zinc ores wherein a selective flocculation step is employed prior to flotation and an ester of a mercaptocarboxylic acid is utilized as a collector during flotation.
It is yet another objective of the present invention to provide a flotation method requiring the addition of substantially smaller amounts of soluble sulfides than heretofore required.